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Abstract

This work attempted optimization of processing conditions of fortified kokoro using response surface modeling (RSM). A central composite rotatable experimental design with three factors (frying temperatures, frying time and cowpea proportions) and five levels was used to evaluate some functional properties and consumer acceptability. The result revealed that solubility, swelling capacity and water absorption capacity of maize-cowpea blend decreased with increase in frying time and temperature. The values obtained for bulk density, swelling capacity, solubility, water absorption capacity and oil absorption capacity ranged from 0.46-0.48 g/mL, 1.27-3.37%, 7.77-10.13%, 171.67-213.33% and 146.67-183.33%, respectively. There was significant difference (p<0.05) in the values obtained for texture, crispiness and taste of fortified kokoro. The desirability value for all the responses was approximately 0.64. The research revealed that varying frying temperature and frying time simultaneously have strong tendency to affect the quality of properties of kokoro fortified with cowpea.

Keywords

Optimazation; Maize; Cowpea Snack; Kokoro; Frying

Introduction

There abound many traditional maize based snacks consumed in many
parts of Nigeria. These include Kokoro (corn-cake), aadun (maize
pudding), donkwa (maize peanut balls) [1]. Kokoro is a traditional snack
consumed especially in western parts of Nigeria. Processing conditions
and proportion of materials are critical in determining the quality of snacks
like kokoro. Kokoro is consumed by categories of people with varying
nutritional demands and therefore suggest the need for nutritional
enhancement. The outcome of inclusion of nutrient aiding food materials
at varying proportion and production conditions may be necessary. The
addition of vegetable protein to improve the nutritional value of snacks
were reported by some researchers [1-3]. Some researchers reported the
quality and nutritional contents improvement of kokoro using beniseed,
cowpea, soybean, groundnut and African yam bean [1,4,5]. Several other
studies have been carried out to improve the protein quality of maize
products by fortification with plant proteins such as cowpea, soybean and
groundnuts [1]. These were, however, done without an attempt to optimise
the process conditions and proportion.

Deep fat frying is an established process of food preparation [6,7]. It often
involves simultaneous heat and mass transfer process. In this process,
moisture is reported to leave the food in form of vapor bubbles and oil is
absorbed simultaneously. In some cases, it is used mainly to activate
unique flavors and texture of processed foods [7,8]. Modification of
physical, chemical and sensory characteristics of the food have been
reported as possible outcome of this operation. Some researchers reported
that temperature and frying time are major variables controlling deep fat
frying operation [7,9,10].

In order to maintain the quality, increase yield and reduce or maintain cost
of production, optimizing the process is very essential. Optimization is
useful in improving the performance of the food system [11]. Optimizing
process and procedure have been reported to aid manipulation of multiple
variables of fewer experimental trials [11,12]. These often result into
developing interactions and models that is capable of aiding efficient and
economic production process. This provide experimental methodology that
help generate a mathematical model that may favorably describe and
predict the process.

The possibility of producing acceptable kokoro with better nutritional
content and sensory quality from maize flour mixed with some legumes
have been attempted by some researchers [1,3-5,13]. This study attempted
the determination of the optimal level of the processing conditions and
cowpea proportion inclusion (Frying temperature, frying time and quantity
of cowpea) using response surface methodology (RSM), which is rare in
previous reported works.

Material and Methods

Maize cultivar (ART 98| SW6-OB) was obtained from Institute of
Agricultural Research and Training in Ibadan, Oyo State, Nigeria. Cowpea
was obtained from Sabo market, Ikorodu, Lagos state, Nigeria. Refined
vegetable oil, salt, onions were obtained from Sabo, Ikorodu, Lagos State.
The maize grains and cowpea were sorted, washed, dehulled manually,
sun-dried and milled using attrition mill (TYPE YL: 112M–4, ATLAS
EXCLUSIVE ALZICO LTD). A deep fat fryer (Model MC-DF 1031) was
used for frying Kokoro. The maize-bean flour blends proportions were
produced according to Box Behnken experimental design of Response
Surface as shown in Table 1. These various blends were packed separately
in 100 μm polythene bags and kept in airtight plastic containers till
needed. Half of each blend was mixed and stirred in boiled water to make
a paste and the remaining half was mixed with salt and onion and then
added to the paste with continuous stirring for about three minutes to form
homogenous thick dough [1,3,14]. The dough was cooled and kneaded.
The kneaded dough was cut into sizes and rolled into ring shapes as
generally practiced with the aid of a chopping board. These rolled out
pieces were deep-fried in hot refined vegetable oil at temperature between
130, 140 and 150°C and frying time 4, 7 and 10 min, respectively. These
were achieved in the combination using a deep fryer for all round frying.
The fried pieces of maize-cowpea snacks with the deep fryer equipment
(Model MC-DF 1031) were drained and left to cool. The proximate,
functional and pasting analyses were conducted on the blends while the
consumer acceptability test was determined on the fried kokoro [15].

TABLE 1Coded values of the independent variables

-α

-1

0

1

+α

X1 (°C)

136.46

130

140

150

143.54

X2 (Min)

5.94

4

7

10

8.06

X3 (%)

92.03

90

95

100

97.97

α=1.4142
X1=Frying Temperature
X2=Frying Time
X3=Maize Proportion.

Experimental Design and Modelling for Optimization

A central composite design with three factors and levels were used. The
three independent variable factors used were frying temperature (X1),
frying time (X2) and beans proportion (X3) and the dependent variable
responses were bulk density, swelling capacity, solubility, water
absorption capacity, oil absorption capacity and the sensory evaluation
parameters (taste, aroma, texture, overall acceptability, colour and
crispiness) and the pasting properties were determined. Twenty frying
trials were performed with eleven central points. The coded value of the
independent variables and treatment schedule are as reported in Table 1.

Determination of Functional Properties

Bulk density determination

The procedure of Narayana and Narasinga [15] was used with slight
modification in the determination for bulk density. The bulk density was
computed as shown in Equation 1.

BULK DENSITY=W/M (1)

Swelling power and solubility

The swelling power and solubility of the maize-based flour samples were
determined using the method reported by Leach et al. [16]. A 1 g of
Maize-based flour was weighed into centrifuge tube and 50 mL distilled
water was added. These tubes were immersed in water bath for 30
minutes, thoroughly and constantly stirred with glass rod during the
heating period. The tubes were removed, cooled to room temperature and
centrifuged at 500 rpm for 15 minutes. The supernatant was fully
transferred into a conical flask and 5ml was pipetted into a weighed petri
dish, evaporated over a steam bath and dried in the air oven at 105°C for 4
hours. The weight of the pastes were determined and used to calculate the
swelling power as gram of sediment paste per gram maize based flour.
Percentage solubility was calculated as gram per gram maize-based flour.

Water and oil absorption capacities

Oil and water absorption capacities were determined, employing the
method described by Beuchat [17] and a 10 mL of distilled water or oil was added to 1 g of sample. The mixture was mixed thoroughly for 30
seconds and allowed to stand for 30 min. The volume of the supernatant
was recorded. The mass of oil or water absorbed were expressed in
percentage.

Sensory evaluation of fortified maize snack (kokoro)

Quality attributes of the kokoro made from maize and beans flour against
a whole maize snack (kokoro) were assessed by 20 member panellists
using 9 point Hedonic scale with respect to taste, aroma, texture, colour,
crispiness and overall acceptability. The scores were ranked and subjected
to statistical analysis.

Model development

Response surfaces were represented mathematically by second-order
polynomial equation to determine the relationship between dependent
variables and independent variables. The model proposed for the response
(Yi) as shown in eqn. [2]

Where X1, X2 and X3 are frying temperature (°C), frying time (min) and
cowpea proportion (%), respectively. b0 is the value of the fitted response
at the centre point of the design (i.e., regression coefficient for
interception), b1-b3, b11-b33 and b12-b23 are regression coefficients for
linear, quadratic and interaction (i.e., cross product terms), respectively. Y
(i=8) is the predicted responses for bulk density, swelling power,
solubility, water absorption capacity, and oil absorption capacity,
respectively [18]. In order to effectively confirm the adequacy and
accuracy of the fitted models, analysis of Variance (ANOVA) was
performed. The use of desirability function of RSM that combine all
responses into one measurement was also employed [18].

Result and Discussion

The bulk density is generally affected by the particle size and had been
reported to have relevant application on packaging, transportation, raw
material handling. The quadratic model with R2=0.55 described the
changes in bulk density of maize-cowpea blends snack (kokoro) during
frying as shown in Table 2. The bulk density of the kokoro ranged from
0.46-0.48 g/mL and there was significant difference (p<0.05) among the
samples as reflected in Table 3. Similar trend was reported by Abegunde
et al. [5]. According to Fasasi et al. [19] the bulk density may be affected
by protein sources and level of supplementation. According to study in
2008, Bulk density of food is very relevant in packaging. The result
revealed that there was significant difference (p<0.05) for Swelling
capacity which ranged from 1.27% to 3.37%. The swelling capacity
obtained was in agreement with values reported by Abegunde et al. [5]
and in contrary to values reported by Ayinde et al. [4]. In this research
work, swelling Capacity decreased with increase in cowpea proportion.

TABLE 2Experimental design and result for functional properties

Trials

Frying temperature(°C)

Frying time (min)

Cowpea Proportion (%)

Bulk density (%)

Solubility (%)

Swelling Capacity (%)

Water Absorption Capacity (%)

Oil Absorption Capacity (%)

1

134.05

5.22

76.08

0.46

8.23

1.8

183.33

151.67

2

145.95

5.22

76.08

0.46

10.13

2.37

196.67

161.67

3

134.05

8.78

76.08

0.46

9.23

1.7

196.67

166.67

4

145.95

8.78

76.08

0.48

9.77

2.37

185

158.33

5

134.05

5.22

93.92

0.48

8.97

2.17

206.67

170.00s

6

145.95

5.22

93.92

0.46

9.57

2.37

205.01

163.33

7

134.05

8.78

93.92

0.48

8.70

1.8

195.00

161.67

8

145.95

8.781

93.92

0.46

9.63

2.37

210.00

183.33

9

130

7

85

0.46

9.63

2.43

211.67

168.33

10

150

7

85

0.48

9.17

2.3

183.33

146.67

11

140

4

85

0.46

8.53

3.23

213.33

160.00

12

140

10

85

0.46

8.67

1.27

171.67

150.00

13

140

7

70

0.46

7.77

1.53

183.33

160.00

14

140

7

100

0.48

9.33

2.13

206.67

168.33

15

140

7

85

0.48

8.90

2.07

196.67

166.67

16

140

7

85

0.46

9.23

2.17

201.67

171.67

17

140

7

85

0.48

9.47

2.03

195.00

166.67

18

140

7

85

0.48

10.1

3.37

186.67

183.33

19

140

7

85

0.48

9.12

1.73

178.33

155.00

20

140

7

85

0.46

8.77

2.27

191.67

166.67

TABLE 3Coefficient of regression for functional properties

Coefficient

Bulk density %

Solubility %

Swelling Capacity %

Water Absorption
Capacity
%

Oil Absorption Capacity %

Model Linear

-11.63

-220.198

-192.47

7063.72

-2623.30

X1(Frying temp)

0.08

-0.62

-0.16

-67.97

54.17

X2(Frying time)

0.04

9.60

-1.28

55.996

-6.32

X3(Beans proportion)

0.13

4.86

4.36

-49.58

-21.62

Quadratic

X11

0.00

701.84

222.13

0.2

-0.26

X22

0.00

-0.11

-0.01

0.65

-2.85

X33

0

-0.01

-0.02

0.18

395.95

Interaction effect

X1X2

6666.67

-0.03

0.02

-0.28

0.33

X1X3

0.00

-0.01

0.00

0.14

0.16

X2X3

0.00

0.03

-0.01

-0.33

39640.20

R2

0.5532

0.3694

0.3997

0.4841

0.3163

F-Value

1.38

0.65

0.74

1.04

0.51

However, the coefficient of regression (R2=0.37) of the quadratic model
and linear were poor fit in the Table 4. Water Absorption Capacity ranged
from 171.67-213.33% and there was significance difference (p<0.5) among samples. This also followed the same trend with the values
reported by Abegunde et al. [5].

TABLE 4Analysis of variance and model fitting for response parameters of maize-cowpea snack(Kokoro)

Df

Bulk density (g/mL)

Solubility %

Swelling Capacity %

Water Absorption Capacity %

Oil Absorption Capacity %

Sequential Model Sum of Squares

Regression

Linear

3

0.00**

1.46

1.43

1141.18**

226.08*

Quadratic

3

0.00

0.65*

0.40*

119.55

274.91

Interaction

3

0.00**

0.33*

0.06*

34.38*

34.69*

Residual Error

6

0.00

2.02

1.61

353.00

585.49

Lack of fit

Linear

11

0.00

4.00**

1.71**

1194.97**

1045.21**

Quadratic

5

0.00**

3.03

1.25

1041.03

735.62

Interaction

8

0.00**

3.68**

1.65**

1160.59*

1010.53**

Pure Error

5

0.00

1.14

1.61

339.04

422.11

*Significantly different at p<0.05.
**Not significantly different at p>0.05.
Df: Degree of Freedom.

It was reported by Houssou and Ayernor [20] that cohesiveness of a
product is strongly dependent on the high water absorption capacity. The
water absorption capacity obtained in this work were lower compared
with reported values by some researchers; Fasasi et al. [19] for fermented
maize flour-tilapia mix, Adetuyi et al. [21] for malted–soya bean (280%) blend and Awoyale et al. [13] for food (kokoro) supplemented with treated
(DSG) (Figure 1).

Figure 1) Surface plot of desirability and frying temperature

Sensory evaluation

The crispiness ranged from 2-3.33 which showed significant difference
(p<0.05) as shown in Table 5. Crispiness increased in frying time and
frying temperature as reflected in Figure 2. The coefficient of progression
R2=0.72 of the model had significant difference (p<0.01) at the linear
model and also showed significant difference (p<0.01), sum of squares
model showed significant difference (p<0.05) at the interaction and
quadratic terms. The texture ranged from 1.93-3.33 showed significant
difference (p<0.05) and overall acceptability increased by increase in
frying time and frying temperature as reflected in Figure 2. However,
kokoro made from 95% maize flour: 5% cowpea flour produced at frying
temperature and time of 140°C and 7-8 minutes were more accepted in
terms of crispness. This followed the trend reported by Awoyale et al. [13]
for kokoro blended with distilled spent grains is shown on the Table 6.

Figure 2: Surface plot of desirability as affected by frying time, frying temperature and cowpea proportion

TABLE 5 Experimental Design and Result for Sensory evaluation

Frying Temperature (°C)

Frying Time (min)

Beans proportion (%)

Taste

Aroma

Texture

Overall acceptability

Colour

Crispiness

134.05

5.22

76.08

2.47

2.47

2.93

2.2

2.33

3

145.95

5.22

76.08

2.8

3.07

2.87

3.27

3.13

3.27

134.05

8.78

76.08

2.6

2.27

2.27

2.13

2.4

2.6

145.95

8.78

76.08

2.4

2.27

2

1.8

2.73

2.33

134.05

5.22

93.92

2.6

2.93

3.07

2.6

2.6

2.93

145.95

5.22

93.92

2.67

2.93

2.93

2.33

2.47

2.8

134.05

8.78

93.92

2.4

3

2.4

2.13

2.17

2.13

145.95

8.781

93.92

3

2.33

2.6

2.33

2.73

2.8

130

7

85

2.93

2.73

3.33

2.8

2.73

2.87

150

7

85

3.13

3

3.4

2.47

2.8

3.33

140

4

85

2.47

2.2

2.4

2.27

2.4

2.2

140

10

85

2.2

2.27

1.93

2.27

2.4

2.27

140

7

70

2.33

2

2.73

2.6

2.2

2.53

140

7

100

3.07

2.73

2.73

2.93

2.6

2.93

140

7

85

2.92

2.73

2.6

2.6

3.13

2.47

140

7

85

2.93

2.8

3.07

2.93

3.13

3

140

7

85

2.27

3

2.6

2.27

2.47

2.87

140

7

85

2.73

3

2.8

2.87

2.73

2.73

140

7

85

1.53

1.67

2.13

1.47

1.93

2

140

7

85

2.07

2.47

2.13

2.2

2.53

2.2

TABLE 6Coefficient of regression for sensory evaluation

Coefficient

Colour

Taste

Aroma

Crispiness

Texture

Overall
Acceptability

Model
Linear

2.58

2.58

2.59

2.54

2.56

2.42

X1(Frying temp)

-

-

-

-5.21

-6.27**

-

X2(Frying time)

-

-

-

-2.12

-0.77

-

X3(Beans proportion)

-

-

-

-2.61

-1.51

-

Quadratic

X11

-

-

-

0.02*

0.02*

-

X22

-

-

-

-0.09

-0.15

-

X33

-

-

-

0.00*

0

-

Interaction effect

X1X2

-

-

-

0.00*

0.00*

-

X1X3

-

-

-

0

0.00*

-

X2X3

-

-

-

0.02

0.02

-

R2

0.00

0.00

0.00

0.50

0.72

0.00

F-Value

0.32

0.32

0.49

1.1

2.87

0.47

The significant level are: *means p<0.1, **means p<0.01.

The desirability functions of RSM were used to determine the optimum
processing conditions of maize snack (kokoro). Optimization was based
on the desirability function; D=(d1×d2×d3×……dn) 1/n. where d1 are the
desirability indices for each response (d1=1; most desirable and d1=0; least
desirable) and n is the number of response used. In this process, responses
that have different scaling are transformed into one measurement useful in predicting the process [22]. The responses were used as the control
parameters, used for determining the optimum quality characteristic with
respect to frying temperature, frying time and quantity of beans proportion
and this as shown in Figures 1 and 2, respectively. When frying time was
set as target, the optimum processing conditions (frying temperature,
frying time, beans proportion) were 140°C, 6.43-6.44 min and
97.93-97.97%, respectively while optimum functional properties (bulk
density, swelling capacity, solubility, water absorption capacity, oil
absorption capacity) were 0.48 g/mL, 2.38-2.39%, 9.26%, 203.7-203.8%
and 170.9-171%, respectively. Also, for optimum sensory evaluation
(taste, aroma, texture, overall acceptability, colour and crispiness) were
2.58, 2.59, 2.71, 2.42, 2.58 and 2.64 respectively. The desirability (0.63)
was obtained for this work. When frying time was set at range, the frying
temperature was set at target and beans proportion was in range, the
optimum processing conditions (frying temperature, frying time, beans
proportion) were 136.46-143.54°C, 7 minutes and 97.86-97.97 %,
respectively while optimum functional properties (bulk density, swelling
capacity, solubility, water absorption capacity, oil absorption capacity)
were 0.47-0.48 g/mL, 2.18-2.33%, 9.18-9.53%, 201.24-201.69%, and
168.05-170.15%, respectively. Also for optimum sensory evaluation
(taste, aroma, texture, overall acceptability, colour and crispiness) were
2.58, 2.60, 2.88-2.96, 2.42, 2.58 and 2.67-2.99, respectively and the
desirability (0.64) was obtained for this work.

When all the processing conditions were set at range, the predicted
processing conditions (frying temperature, frying time, beans proportion)
in the Figures 1 and 2 were 136.46–143.54°C, 6.04–6.73 minutes and
97.78–97.96% respectively while optimum functional properties (bulk
density, swelling capacity, solubility, water absorption capacity, oil
absorption capacity) were 0.47-0.48 g/mL, 2.32-2.50%, 9.01-9.56%,
203.64-209.15% and 166.12-169.03%, respectively. Also for optimum
sensory evaluation (taste, aroma, texture, overall acceptability, colour and crispiness) were 2.58, 2.59, 2.92-2.99, 2.42, 2.58 and 2.69-3.00,
respectively and the (0.64) was obtained for this work.

The point with highest possible desirability (0.64) function that could be
taken as the optimum condition for frying temperature and frying time combination of maize snack (kokoro) was found to be 143.54°C and 7
minutes, respectively as shown in Figure 3.

Figure 3) Response surface desirability of processing condition

Conclusion

Frying of maize snack (kokoro) at different temperature and time with the
combination of beans in different proportions affected the general
properties of kokoro. The Fortification of maize snack (kokoro) has strong
tendency to improve its nutritional content however, have effect on the
functional properties. the Predicted frying temperature, time and beans
proportion of 143.5°C, 7 minutes and 98%, respectively with the
functional properties 0.47 g/mL (bulk density), 2.3%(swelling capacity),
9.5% (solubility), 201.7% (water absorption capacity), 2.58 (taste),
2.60(aroma), 2.88-2.96 (texture), 2.42 (overall acceptability), 2.58
(colour) and 2.67-2.99 (crispiness) gave the highest desirability value.

References

Rosa N, Chavez-jauregui RAC, Marian EM, et al. Acceptability of snacks produced by the extrusion of Amaranth and blends of chicken pea and bovine lung. International Journal of Food Science and Technology.2003;38:795-98.